A subject matter of the present invention is a process for the condensation of aromatic derivatives and of a sulfinic derivative, the carbonaceous chain of which is attached to the sulfinic functional group via a perhalogenated carbon atom. It relates more particularly to a process for the synthesis of reactants of the type of those developed, firstly, by Professor Yagupol""skii and his team and then by Professor Umemoto and his team.
This perfluoroalkylating reagent exhibits, as alkylating functional group, a sulfonium substituted by two aryls, or an aryl and an alkyl unit, and a perfluoroalkyl.
Access to this type of functional group is particularly difficult. This type of functional group is currently obtained by the action of an aryl perfluoroakyl sulfoxide, which is condensed with an aromatic derivative in the presence of strong acid.
It is the above sulfoxides which present the most difficulties in being synthesized.
The syntheses described by Pr. Yagupol""skii and his team (see in particular Zh. Org. Khim., vol. 20, No. 1, p. 115 to 118, January 1984) and Pr. Umemoto and his team (see in particular Chem. Rev., 1996, 96, p. 1757 to 1777) are both lengthy and difficult.
This is not very surprising, due to the many side reactions which take place in these extremely acidic and relatively unstable media.
This is why one of the aims of the present invention is to provide a process which make possible the synthesis of sulfoxide connected, on the one hand, to a perfluoroalkyl group or more generally to a group exhibiting a perhalogenated carbon atom connected to the sulfoxide functional group and, on the other hand, to an aryl radical.
Another aim of the present invention is to provide a process which makes it possible to obtain perfluoroalkyl diaryl sulfonium.
Another aim of the present invention is to provide a process of the preceding type which makes it possible to link together, in the same reactor, the preparation of the sulfoxide and then of the perfluoroalkyl diaryl sulfonium.
These aims and others which will become apparent subsequently are achieved by means of a process for the condensation of aromatic derivatives and of a sulfinic derivative, the carbonaceous chain of which is attached to the sulfinic functional group via a perhalogenated carbon atom, advantageously a perfluorinated carbon atom, in which process said sulfinic derivative and said aromatic derivative are subjected to the action of a strong acid, the pKa of which is at most equal to zero.
At the present time, this type of reaction can hardly be explained but by the existence in the reaction medium of a protonated form of the sulfinic functional group, a form whose presence is highly improbable and very surprising because of the extreme acidity of perhalosulfinic acids.
Said sulfinic functional group can be chosen in particular from acid, salt or ester functional groups. It is also possible to envisage mixed anhydride functional groups, including acid halides. However, these compounds exhibit the disadvantage of not being very stable and require significant operating precautions.
The forms which directly generate the acid (that is to say, the acid itself and the salts) are preferred.
The acids capable of giving the reaction are chosen in particular from hydrohalic acids, advantageously including sulfonic acids, preferably perhalosulfonic acids, and fluorosulfinic acids, sulfuric acid and their mixtures.
During the study which led to the present invention, it was shown that the presence of water played a significant role in the implementation of the reaction.
Excess water has a tendency to block any reaction; on the other hand, the complete absence of water is capable of promoting undesired side reactions, in particular polymerizations.
Thus, according to the present invention, it is preferable to keep the amount of water involved during the reaction within a restricted range.
It has thus been shown that it is preferable for the H2O/sulfinic functional group molar ratio to be at most equal to 4, advantageously to 3, preferably to 2.
At the other boundary of the range, it is preferable for the H2O/sulfinic functional group ratio to be at least equal to 0.1, advantageously to 0.2 and preferably to 0.5.
The optimum region is thus within approximately 2 and approximately 0.2 for the H2O/sulfinic functional group molar ratio.
Another constraint can be significant as regards the amount of water in the medium.
Thus, if the H2O/strong acid functional group molar ratio is examined, it is preferably at most equal to 2 or better still at most equal to 1 but it has been shown that it is desirable for it to be at least equal to 0.05, advantageously to 0.1, preferably to 1/4.
To solve these problems, it may sometimes be useful to carry out the reactions in the presence of a dehydrating agent.
It is possible to use phosphorus pentoxide (P2O5) as dehydrating agent. It is also possible to envisage using oleum. However, one of the best dehydrating agents is composed of the symmetrical or mixed anhydrides of perfluoroalkanesulfonic acids. These acids, the commonest of which is the paradigm, is trifluoromethanesulfonic acid, alias triflic acid.
According to the present invention, the reaction can be carried out without a solvent, that is to say that one or more of the components of the reaction mixture, in excess or not in excess, constitutes the solvent.
However, it is possible to envisage solvents for this type of reaction, namely solvents of low basicity. This is because basic solvents, on the one hand, are unstable in the presence of strong acids, such as triflic acid, and, on the other hand, reduce the acidity thereof.
Thus, according to the present invention, it is preferable to use solvents exhibiting a low donor number.
Mention may be made, as examples of organic solvents which can give good results, of halogenated solvents, aliphatic solvents and aromatic solvents which are highly depleted in electron, and their mixture.
One of the advantages of the present invention is that it can be carried out in a fairly wide temperature range. Thus, the invention is advantageously carried out at a temperature at most equal to 100xc2x0 C., preferably to 80xc2x0 C., more preferably to 50xc2x0 C.
It is also desirable for the temperature to be at least equal to the starting melting point, preferably finishing melting point, generally at least equal to 0xc2x0 C.
The reaction is generally carried out at atmospheric pressure but it can easily be carried out under a higher or lower pressure than atmospheric pressure. The choice of the pressure depends on the reaction medium and on its boiling point.
When an ester is used as sulfinic functional group, it is preferable for the alcohol to be a primary alcohol, advantageously a C1-C4 alcohol.
As regards them, it should be pointed out that the richest substrates, such as anisol, give mediocre results; this is perhaps due to side reactions related to the rich doublet of the oxygen.
On the other hand, very good results are obtained with relatively slightly enriched nuclei, such as alkylbenzenes, or relatively slightly depleted nuclei, such as benzene nuclei substituted by halogens; highly depleted aromatic nuclei are needed for a significant fall in the reactivity, as in the case of trifluoromethylbenzenes.
Said carbonaceous chain is advantageously a radical described as a perfluoroalkyl (Rf) radical; this term is preferably understood to mean radicals of formula:
xe2x80x94(CX2)pxe2x80x94EWG
where
the X groups, which are alike or different, represent a halogen (advantageously represents at least one fluorine, preferably at least 2, per carbon) or a radical of formula CnF2n+1 with n an integer at most equal to 5, preferably to 2;
where p represents an integer at most equal to 2;
where EWG represents an electron-withdrawing group, the possible functional groups of which are inert under the reaction conditions, advantageously fluorine or a perfluorinated residue of formula CnF2n+1 with n an integer at most equal to 8, advantageously to 5.
The total carbon number of Rf is advantageously between 1 and 15, preferably between 1 and 10.
Some of the compounds synthesized in the examples are novel compounds.